Can I revoke my purchase within 14 days?

No, unfortunately this is not possible.

The reason: Unlike online purchases of clothing or electronics, the statutory right of withdrawal does not apply to contracts for the transport of persons (pursuant to § 312 Abs. 8 BGB, German Civil Code). Since the ticket is digital and immediately valid and usable upon issuance, it cannot be "returned."

What you can do: While you cannot retroactively cancel the current ticket, you do have the option to pause or cancel the subscription in time for the next month (except in the first month after the 10th).